The present invention relates generally to implantable medical devices for monitoring internal physiological conditions of a patient, and, more particularly, to a biosensor that is attachable to a prosthesis for remotely monitoring physiological conditions of a patient, such as pressure within an aneurysm cavity across which a prosthesis is implanted.
An aneurysm is a weakening of a wall of a blood vessel that generally results in a ballooning of the wall, and, if left untreated, may result in a rupture that may seriously threaten the life of a patient. The weakening of the wall may be due to injury, infection, or other conditions, such as a congenital defect in the arterial connective tissue. Common forms of such an aneurysm include an abdominal aortic aneurysm (xe2x80x9cAAAxe2x80x9d), an iliac aneurysm, a bifurcated aneurysm of the abdominal aorta and one or both of the iliac arteries, and a thoracic aortic aneurysm.
To treat a patient suffering from an aneurysm, a tubular prosthetic graft may be implanted across the aneurysm using an open surgical technique to substantially isolate the weakened region of the vessel from adjacent healthy regions. For example, the vessel wall may be cut longitudinally along the vessel wall, the graft inserted and anastomosed coaxially within the vessel as an internal replacement for the diseased segment, and then the longitudinal cut may be sutured closed. Alternatively, opposite ends of a prosthetic graft may be sutured to a vessel on either side of the weakened region to form a bypass conduit around the diseased segment. Such surgical approaches, however, may involve extensive recovery times, may be complicated because of the difficulties in suturing the graft to the vessel, and/or may be unsuitable for many at-risk patients because of the high mortality and morbidity rates associated with a surgical intervention of this magnitude.
As an alternative to open surgery, endolumenal stent graft implantation has been suggested. An endolumenal stent graft generally includes a vascular graft and a support structure, such as a self-expanding or balloon-expandable stent, that may engage each end of the graft or may extend along all or a portion of a length of the graft. The stent graft may be introduced percutaneously into the patient""s vasculature in a reduced profile, for example, on or in a delivery catheter. The stent graft may be advanced to a treatment site, such as a damaged segment of the abdominal aorta, and placed across the treatment site. The support structure may then be radially expanded, anchoring the graft to the healthy regions of the vessel adjacent the damaged segment, and substantially sealing the aneurysm from the rest of the circulatory system. As a result, pressure within the isolated aneurysmal sac may be reduced, thereby reducing stress or xe2x80x9cendotensionxe2x80x9d on the weakened wall of the vessel. Endotension is a physical parameter that may indicate the likelihood of an aneurysm rupturing, and is generally defined in terms of the internal pressure within the aneurysm, the aneurysm diameter and vessel wall thickness.
One potential complication that may occur after a stent graft is implanted is the formation of an endoleak. Endoleaks may be divided into four categories: leakage due to improper sealing of the graft against the vessel wall (Type I), blood flow into the aneurysmal sac through bypass arteries (Type II), leakage due to mechanical failure of the graft system (Type III), and leakage through the graft due to the porosity of the graft material (Type IV).
If fluid leaks into the aneurysmal sac, it may increase the pressure or endotension within the aneurysm, possibly resulting in an aneurysmal rupture. To substantially reduce the risk of this occurring, early detection of endoleaks or endotension may be important. With early detection, the pressure within the aneurysmal sac may be reduced by subsequent endovascular treatment (for example, further expansion of the stent graft support structure, or additional stent graft implantation to improve sealing), or, if necessary, surgical intervention.
Currently, contrast-enhanced computerized tomography (CT) is often used to detect endoleaks, which relies on x-ray imaging of an abdominal region after injection of a contrast media. If an endoleak is present, the aneurysmal sac may fill with contrast media and the endoleak may then be identified by the CT scan. Although CT scans are considered a reliable method for detecting endoleaks, they require an experienced operator and an expensive apparatus, placing significant financial constraints on its frequency of use. In addition, a CT scan procedure exposes the patient to x-ray radiation, and thus may only be recommended every 3 to 6 months following stent graft implantation. Finally, because CT scans only detect actual leakage and not pressure within the aneurysm, they may not detect small leaks that may cause slow, but potentially dangerous, pressurization within the aneurysm.
As an alternative to CT scans, ultrasound imaging may be used to detect endoleaks. Ultrasound imaging uses a simpler apparatus, resulting in a potential cost savings over CT scanning, and does not involve the use of ionizing radiation and its associated risks. The quality of ultrasound imaging, however, may be more operator dependent, and therefore may be less reliable than CT scans.
Accordingly, it is believed that a system and method for monitoring internal pressure within an aneurysmal sac may be considered useful.
The present invention is directed to apparatus and methods for implanting a biosensor, preferably in conjunction with an endoprosthesis, within an abdominal aortic aneurysm or other enlarged or weakened treatment site within a body lumen of a patient.
In accordance with a first aspect of the invention, an apparatus for monitoring a physical parameter at a treatment site within a body lumen is provided. The apparatus includes a tubular prosthesis expandable between a contracted condition for facilitating introduction into the body lumen, and an enlarged condition for contacting a wall of the body lumen at the treatment site. A substantially enclosed loop having a size for substantially securing the loop around the prosthesis in its enlarged condition is provided with a biosensor attached to the loop.
In one preferred embodiment, the loop may be a ring or sleeve formed from a substantially elastic material, the ring or sleeve having a relaxed state having a cross-section smaller than the prosthesis in its enlarged condition. In an alternate preferred embodiment, the loop may be a substantially inelastic, flexible thread having a cross-section similar to the prosthesis in its enlarged condition.
In accordance with another aspect of the invention, an apparatus is provided for delivering the biosensor device to a treatment site within a body lumen. The apparatus includes an elongate member having a proximal end and a distal end adapted for introduction into the body lumen, and a connector located on the distal end of the elongate member for detachably securing the loop to the distal end of the elongate member. Preferably, an actuator is provided on a proximal end of the elongate member for detaching the loop from the connector. In preferred embodiments, the apparatus may also include a sheath slidable over the elongate member or other constraint for constraining the loop to facilitate its introduction into the body lumen.
By way of example, in one preferred embodiment, the connector is a wire having a first end extending from the proximal end of the elongate member, and a second end extending to the distal end of the elongate member. The wire may be intertwined with the loop to thereby substantially secure the loop to the distal end of the elongate member. The actuator preferably is a handle on the first end of the wire for pulling the second end of the wire from the distal end towards the proximal end, thereby releasing the loop therefrom. The loop may include a ring for receiving the wire therethrough.
In accordance with still another aspect of the invention, a delivery device is provided for directing the prosthesis to the treatment site in its contracted condition. The delivery device preferably has a cross-section substantially smaller than a cross-section of the loop, thereby facilitating positioning the loop coaxially with respect to the prosthesis before the prosthesis is deployed from the delivery device.
In accordance with yet another aspect of the invention, a method is provided for implanting a biosensor at a treatment site within a body lumen. In a preferred implementation, a tubular prosthesis is advanced in a contracted state within the body lumen to the treatment site, for example, mounted to a delivery device. A loop is also advanced to the treatment site, the loop including a biosensor attached thereto. Preferably, the loop is detachably connected to a delivery apparatus that is used to advance the loop to the treatment site. The loop may be deployed from a compressed state on the delivery apparatus once advanced to the treatment site, and manipulated to assume an open configuration across the treatment site.
In one preferred embodiment, the loop may be expanded across the treatment site before the prosthesis is advanced to the treatment site, and the prosthesis may be advanced through the loop upon advancement of the prosthesis to the treatment site. Alternatively, the loop may be advanced coaxially over the delivery device to the treatment site.
Preferably, the loop and the prosthesis may be positioned coaxially with respect to one another at the treatment site. The prosthesis may then be expanded towards an enlarged condition, thereby substantially engaging the loop around the prosthesis and substantially engaging the prosthesis to a wall of the blood vessel at the treatment site. Once the prosthesis is expanded, the loop may be released from the delivery apparatus, and the apparatus withdrawn from the patient. As a result, the biosensor is disposed within an aneurysmal sac at least partially defined by the aneurysm. The biosensor may then be used to remotely monitor the aneurysmal sac to detect pressure, leaks or other desired physical conditions therein.
Other objects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings.